Purpose: In this study, we investigated the migration of enterohemorrhagic Escherichia coli (EHEC), artificially internalized into vegetable seeds, to different sprout/seedling tissues during seed germination and seedling emergence.
Methods: Nalidixic acid-resistant EHEC (K4492, H1730, ATCC BAA-2326 and F4546) were artificially infiltrated into alfalfa, fenugreek, lettuce, and tomato seeds using vacuum. Contaminated seeds were germinated on 1% water agar in germination boxes at 25°C for nine days. Ten replicate samples of each seed section, including whole seed, seed coat, cotyledon, stem, and root were collected twice daily. Seed sections were homogenized and aliquots of homogenates were plated, in duplicate, on sorbitol MacConkey agar and tryptic soy agar supplemented with nalidixic acid. The experiment was repeated once and results were analyzed by Fisher’s LSD test using the R software.
Results: Cells of all four E. coli strains migrated from contaminated seeds to different sprout/seedling tissues. Approximately 67% of the 512 collected seed sections tested positive for E. coli. The average population of E. coli increased from 0.64 to 1.34 log CFU/seed section during seed germination. On average, the E. coli count on whole seeds was significantly lower than the counts from other seed tissues, which were not significantly different from each other (P>0.05). The average populations of the four E. coli strains on sprouts and seedlings were not significantly different (P>0.05). Escherichia coli counts from alfalfa and fenugreek sprouts (1.81 and 1.34 log CFU/seed section, respectively) were significantly higher (P<0.05) than those from lettuce and tomato seedlings (0.17 and 0.26 log CFU/seed section).
Significance: This study revealed the ability of EHEC to migrate from internal seed tissues to different areas of sprouts/seedlings during germination. It emphasizes the importance of using pathogen-free seeds for commercial vegetable sprout production.